Technical Abstract:
Six different biological amendments were evaluated for their effects on the development of soilborne diseases of potato and compared to a nontreated control treatment in a field test at Newport, ME in 2007. The biological amendments consisted of: 1) a bacterial biocontrol agent (Kodiak; Bacillus subtilis); 2) a fungal biocontrol agent (CX-2250; Trichoderma virens); 3) a mixture of beneficial microorganisms (Compete Plus; containing Bacillus spp., Streptomyces griseoviridis, and Trichoderma harzianum); 4) an aerated compost tea made from vermi-compost (ACT; 24-hr brew); 5) a mixture of arbuscular mycorrhizal fungi (AMF); and 6) a green clay formulation (Agriclay A6). Compete, ACT, and AMF treatments significantly reduced the incidence and severity of black scurf on tubers, caused by Rhizoctonia solani, with reductions of 15-50% relative to the nontreated control. ACT and AMF also reduced the incidence and severity of common scab, caused by Streptomyces scabiei, by 19-43%. Compete and CX-2250 also reduced the severity (10-15%), but not incidence of common scab. Kodiak and Agriclay did not reduce development of either disease. Tuber yield was not significantly affected by any treatment, although ACT and CX-2250 resulted in the nominally highest yields. There also were no significant treatment effects on the distribution of tuber size classes or marketable yield. These results indicate that biological amendments containing mixtures of beneficial microorganisms, such as Compete, compost tea, and mycorrhizal inoculants, can effectively reduce soilborne diseases of potato.